One of the most successful and enduring feats of interplanetary exploration, NASA's Opportunity rover mission is at an end after almost 15 years exploring the surface of Mars and helping lay the groundwork for NASA's return to the Red Planet.

Apollo 17 astronauts drove a moon buggy across the lunar surface in 1972, measuring gravity with a special instrument. There are no astronauts on Mars, but a group of clever researchers realized they have just the tools for similar experiments with the Martian buggy they're operating.